This invention relates to wire matrix print head apparatus of the general type disclosed in prior U.S. Pat. Nos. 3,929,214 and 3,994,381.
In general, this invention provides a wire matrix print head assembly and apparatus which is less costly to manufacture and more reliable in operation while also being more efficient, less noisy, and having higher energy potential than prior art apparatus.
In prior art apparatus, such as that disclosed in the afore-identified United States patents, wire type printing members (stylus or styli) are arranged in spaced relationship about a central longitudinal axis in a generally circular or elliptical matrix for reciprocable movement between a non-print position and a print position with the movement from the non-print position to the print position being of ballistic nature, i.e. by impact and/or driving engagement with another moving member. Each printing member is operatively associated with a radially innermost portion of a radially outwardly extending armature member and ballistically driven thereby by impact therewith during pivotal movement of the armature from a non-print position to a print position. A radially outermost portion of each armature is operatively associated with a radially outwardly located and circumferentially spaced electromagnetic means having radially spaced pole portions including a radially innermost pole portion and a radially outermost pole portion, the pole portions including flat coplanar radially spaced and radially extending end surfaces which face away from the direction of movement from the non-print position to the print position and engaging a side surface of the armature at various times. In the prior art apparatus, the construction and arrangement is such that the armature is pivotally supported at all times on a radially outermost edge of the end surface of the radially outermost pole portion and impacts the end surface of the radially innermost pole portion which is constructed and arranged to cause pivotal movement of the armature from the non-print position to the print position by magnetic attraction. In addition, the construction and arrangement is such that the armature impacts on the end surface of the innermost pole portion at approximately the same time that the printing member is being driven toward the paper. The result is that the kinetic energy of the armature is lost and only the kinetic energy of the printing member is thereafter effective to cause completion of the printing operation. In fact, of the kinetic energy available just prior to impact of the armature with the surface of the pole portion, approximately two-thirds is lost through armature impact with only approximately one-third remaining in the printing member to accomplish the printing operation. The lost two-thirds of the available kinetic energy is simply dissipated upon impact with the surface of the pole portion with resultant high levels of noise and heat. In addition, the speed of the printing process is reduced and the number of sheets of paper which can be printed at one time is also limited. Furthermore, in order to obtain sufficiently high levels of kinetic energy to produce satisfactory printing results, relatively high levels of energy must be used to operate the electromagnetic means.
In the present invention, the armature members and the electromagnetic means are constructed and arranged so that the armature members are normally pivotally supported by a first pivot means on a radially innermost edge of a radially innermost pole portion while being magnetically attracted by a radially outermost pole portion. In addition, the pole portions are constructed and arranged so that the end surfaces thereof face toward the direction of movement of the armature and the printing members from the non-print position to the print position. As a result, the driving movement of the armature continues after impact with the end surface of the outermost pole portion without loss of a substantial portion of the kinetic energy thereof as in prior art apparatus. Furthermore, in the present invention, the construction and arrangement is such that after impact of the armature with the end surface of the outermost pole portion, the first pivot means is disengaged and a second pivotal means is provided between a radially outermost portion of the armature and the radially outermost edge of the radially outermost pole portion whereby the driving movement of the armature may continue substantially unimpeded until completion of the printing operation.
In addition to the foregoing advantages, the present invention further provides for new and improved mounting of the apparatus including the use of housing means made of one piece of molded plastic material which mounts and supports all of the apparatus in a new and improved manner. The electromagnet means comprises a one piece member of sintered powder metallic material providing an end plate having the pole portions integral therewith. Also, the one piece electromagnet member is mounted on the one piece housing means in a manner requiring only one threaded fastening means which may be readily adjusted to vary the axial air gap between the end surfaces of the pole portions and the armature as well as adjusting the armature movement.